Hey guys! So following EEVBlog's example, I wanted to control Nixie tubes using the TPIC6B595 shift register. The schematic I used is attached. Basically, the Anode of the nixie is connected to a 180 VDC supply via a 3 K ohm resistor, and the digit leads are connected to the 8 output pins of the shift register. I'm powering the shift register using my board's 5V pin. I power the arduino separately using my USB cable. But when I turn on the 180 VDC power, the board blows up! I've triple checked for shorts and other anomalies, but I can't find anything awry. I tried with another Uno board and the same thing happens. What could be the issue? On both boards, the place where it blows up is somewhere around the area highlighted with the red circle. Strangely enough, the voltage regulator is unaffected. The code I'm using is also given below:
#define DATA 11
#define LATCH 10
#define CLOCK 12
int digits[] = {
B00000000,
B00000010,
B00000100,
B00001000,
B00010000,
B00100000,
B01000000,
B10000000};
int i;
void setup() {
pinMode(DATA, OUTPUT);
pinMode(LATCH, OUTPUT);
pinMode(CLOCK, OUTPUT);
Serial.begin(9600);
}
void loop() {
for (i = 0; i < 8; i++) {
//Serial.println(i);
digitalWrite(LATCH, LOW);
shiftOut(DATA, CLOCK, MSBFIRST, digits[i]);
digitalWrite(LATCH, HIGH);
delay(500);
digitalWrite(LATCH, LOW);
shiftOut(DATA, CLOCK, MSBFIRST, digits[0]);
digitalWrite(LATCH, HIGH);
delay(500);
}
i =0;
}
So following EEVBlog's example, I wanted to control Nixie tubes using the TPIC6B595 shift registe
Please provide a link to the entry where the guy connects 180V directly to a TPIC6B595. A short search just showed entries where he explicitly says the he uses external high voltage transistors for that. The TPIC has dropout voltage of 50V, so probably the 180V go through it and blow the 3V3 regulator or the LM358 operational amplifiers on the UNO board.
pylon:
Please provide a link to the entry where the guy connects 180V directly to a TPIC6B595. A short search just showed entries where he explicitly says the he uses external high voltage transistors for that. The TPIC has dropout voltage of 50V, so probably the 180V go through it and blow the 3V3 regulator or the LM358 operational amplifiers on the UNO board.
Here's the video where he discusses the schematic. It's similar to my schematic. He mentions that the TPIC has a zener clamp which clamps the voltage across the TPIC.
But in my case, where do you suggest I have the high voltage transistors? What changes in the schematic?
The trick with Nixie tubes is their different voltage drop in ON and OFF state. At least one digit must be ON, sinking current and thus reducing the anode voltage. The other OFF digits drop much voltage, so that their cathode voltage can become 50V and less, what is affordable to transistors. But if no digit is ON, a high cathode voltage can damage everything connected.
For testing purposes you can connect a Nixie tube anode to the HV power supply, one cathode to Gnd, and then measure the voltage on the other (OFF) cathodes. This voltage is what a Nixie driver must support at least. Eventually you reduce the anode supply voltage to less than 180V, the voltage only must be high enough to fire one digit.
The dedicated Nixie drivers (74141) have zener diodes on all outputs that limit the voltage to acceptable values. If all digits are OFF, they may glow dimly due to these zener diodes.
DrDiettrich:
The trick with Nixie tubes is their different voltage drop in ON and OFF state. At least one digit must be ON, sinking current and thus reducing the anode voltage. The other OFF digits drop much voltage, so that their cathode voltage can become 50V and less, what is affordable to transistors. But if no digit is ON, a high cathode voltage can damage everything connected.
For testing purposes you can connect a Nixie tube anode to the HV power supply, one cathode to Gnd, and then measure the voltage on the other (OFF) cathodes. This voltage is what a Nixie driver must support at least. Eventually you reduce the anode supply voltage to less than 180V, the voltage only must be high enough to fire one digit.
The dedicated Nixie drivers (74141) have zener diodes on all outputs that limit the voltage to acceptable values. If all digits are OFF, they may glow dimly due to these zener diodes.
That's it!!! In my code, I turn OFF all the nixies half the time, while turning ON one of them in the other half. This might have been the problem.....I think if I change my code to instead keep one digit ON at all times would avoid this problem. Thanks!!! I'll test this out and let you know!
sreshtiyer:
I think if I change my code to instead keep one digit ON at all times would avoid this problem.
That is an obvious imperative, but you have to consider the requirement to initialise the TPIC6B595 - which is to say, have the microcontroller up and running - before you turn on the 180 V and not shut down the logic supply while the 180 V is active.
May be easier to have a 47 V Zener bridging the TPIC6B595 output to each "0" cathode.
Paul__B:
That is an obvious imperative, but you have to consider the requirement to initialise the TPIC6B595 - which is to say, have the microcontroller up and running - before you turn on the 180 V and not shut down the logic supply while the 180 V is active.
May be easier to have a 47 V Zener bridging the TPIC6B595 output to each "0" cathode.
Even so I suspect a wiring fault.
That I did make sure of. I always turned it on when the microcontroller was ON first. But the code was still blanking all the Nixie digits for 500 ms and then turned on 1 of them for 500 ms. This time, I can modify the code to shuffle from 1 output to the last without actually turning them off. I would have added a zener clamp, but since I;ve already hardwired everything, desoldering everything would be a pain in the ass. I really should have tested them on a breadboard first
Well guys, thanks a lot for all your help! Once I added the correct series resistance to the nixie, and also making sure I don't turn off all the outputs at once, I was able to finally make it work! I also made sure not to use the mains power supply, and instead switched over to a 12 V to 180 V DC boost converter circuit using the MC34063 chip. It seems to work now!
DrDiettrich:
The dedicated Nixie drivers (74141) have zener diodes on all outputs that limit the voltage to acceptable values. If all digits are OFF, they may glow dimly due to these zener diodes.
The TPIC6x595 has that too (active clamping).
Different clamp voltage for different TPIC chips.
The 'B' version is 50volt.
Leo..
